Effects of heat treatments on the microstructure and hardness of thermally sprayed Ni-Cr-Mo-Al alloy coating

Abstract

Thermal spray coating is one of the technologies used to prevent corrosion and wear by creating a protective layer on the substrate. From previous research, the microstructure of arc-sprayed nickel-chromium-molybdenum-aluminium (Ni-Cr-Mo-Al) after heat treatment at 1100°C was investigated. It was found that the corrosion rate of this coating under 20vol%H2SO4 was reduced by 97%. However, the heat treatment at high temperatures is still limited to industrial applications. Therefore, this research will focus on studying microstructure and properties after heat treatment at moderately high temperatures, which are in a range of service temperature. Specimens were arc sprayed and heat treated at 300, 400, 500, 600 and 700°C and characterized by Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray Spectroscopy (EDS) technique. Phases were analyzed by X-ray diffraction (XRD). There was no significant change of γ-Ni grains after heat treated at 600°C for 10 days from the Electron Backscattered Diffraction (EBSD) study. The hardness of the coatings increased after heat treatments due to a reduction in porosity, an increase of oxides and the formation of MoSi2.